Organic electroluminescence devices (hereinafter also referred to as “organic EL device”) have been known, in which an organic thin film layer including a light emitting layer is disposed between an anode and a cathode, and the energy of exciton generated by the recombination of hole and electron which are injected into a light emitting layer is converted into light.
Utilizing its advantages as the spontaneous emitting device, the organic EL device has been expected to provide a light emitting device excellent in the emission efficiency, the image quality, the power consumption, and the freedom of design. It has been known to make the light emitting layer into a host/dopant emitting layer in which a host is doped with an emission material as a dopant.
In a host/dopant emitting layer, excitons can be efficiently generated from charges injected into a host. The energy of generated excitons is transferred to the dopant, and the light emission from the dopant with high efficiency can be obtained.
To improve the performance of organic EL devices, the recent study is directed also to the host/dopant system, and the search for a suitable host material and other materials for organic EL devices has been continued.
The method for forming each layer of an organic EL device is classified roughly into a vapor deposition method, such as a vacuum vapor deposition method and a molecular beam evaporation method, and a coating method, such as a dipping method, a spin coating method, a casting method, a bar coating method, and a roll coating method. The material for use in forming the layer by a coating method is required to satisfy the properties not required in the material for use in the vapor deposition method, for example, temperature resistance and solubility in solvents. Therefore, a material useful in the vapor deposition method is not necessarily useful in the coating method. In addition, the material is required to be capable of forming the layer by a coating method and further required to meet various performances necessary for organic EL devices.
Particularly, since the coating method for forming the layer is applicable to the production of a large-sized organic EL display and lighting panel, an material for organic EL devices applicable to the coating method has been desired to develop.